Reasons to believe Lucien Draay becomes Darth Sion:
-The events depicted in The Knights of the Old Republic comic take place before and during the Mandalorian Wars. Therefore, they occur before the KotOR video games.
-Master Vandar called him the "scion of an important family."
-Haazan considers calling Lucien "Darth Sion."
-Lucien survives the destruction of the Draay estate, although his eyes are damaged and his hands burned in a way that resembles Darth Sion's cracked hide.
-Lucien contemplates the possibility of becoming a "Lord of Pain."

Now, I know that many will say that Lucien was just a toddler, because Sion was, logically, already a grown adult serving Exar Kun. So it's impossible for Lucien to have become Sion.

However, there is a Sith relic that can transport you back in time(Darkstaff) It has already happened once.

Who is to say Lucien didn't go back in time to serve under the Dark Lord Exar Kun and to make a name for himself?

__________________The Ellimist: "Nadd is the 90 IQ guy who acts like a 70 IQ guy to make fun of the nerds"

I remember there were a lot of theories floating around on the Jedi Council forums about Zayne=Nihilus, Lucien=Sion, Krynda=Kreia and the comic itself hinted at those connections sometimes but nothing ever came of it.

However, there is a Sith relic that can transport you back in time(Darkstaff) It has already happened once.

Who is to say Lucien didn't go back in time to serve under the Dark Lord Exar Kun and to make a name for himself?

whoa, whoa, whoa there. What's this darkstaff, and what story did it appear in? I've honestly never heard of it until now.

With that out of the way. It is straight up impossible for Lucien to be Darth Sion. Sion did not have the gauntlet that Lucian had at the end of Knights of the Old Republic. In addition to this in STAR WARS: THE CLONE WARS - DEFENDERS OF THE LOST TEMPLE, it's outright revealed the Lucien made a new Jedi temple and hid the guantlet there. Finally Darth Sion was terrible at fighting multiple opponents. He died like 3 times in the first confrontation with Mitra Surik alone. I'm forgetting the name of Lucien's saber style, but it literally made him better at fighting multiple opponents.